14 
Le Floch - What are Dispersants? 
into a multitude of oil droplets in suspension in the water column. From an operational point 
of view, chemical dispersion: 
1. transforms the hazards inherent to the oil slick by eliminating the risk of responders 
being exposed to a toxic or even explosive cloud, and by reducing the exposure of 
birds and marine mammals; 
2. reduces the amount of oil which will wash up on the shoreline and therefore 
downscales shoreline clean-up operations, reduces the production of waste which re 
quires specialised treatment and decreases the amount of oil buried in the sediment 
matrix; 
3. promotes the assimilation of the oil by the environment, in particular by increasing its 
dilution and final degradation by micro-organisms naturally present in the environ 
ment. 
Characteristics of dispersant 
Dispersants are liquids that are sprayed onto an oil slick at the sea surface in order to facili 
tate the natural dispersion of the oil in the water column. In fact, the natural dispersion of oil 
droplets in the sea water column can be observed if enough energy is present at the sea 
surface (e.g. waves) and dispersants will increase this phenomenon. In addition, suspended 
oil droplets have a smaller diameter which will cause an increase in the contact surface be 
tween oil and water. 
Chemical composition 
By definition, dispersants are blends of surfactants in solvents. By reducing the interfacial 
tension between oil and water, surfactants enable these two phases to mix with each other 
more easily. Surfactants are usually organic compounds that are amphiphilic, meaning they 
contain both hydrophobic groups (attract oil) and hydrophilic groups (attract water). There 
fore, a surfactant contains both a water-insoluble (or oil-soluble) component and a water- 
soluble component (Figure 4.1). Even though there are thousands of individual surfactants, 
only a few (usually non-ionic surfactants) are used in dispersant products. 
attracts 
water 
► 
attracts 
oil 
water 
surfactant 
Figure 4.1 : Structure of a surfactant and Interaction of surfactant with oil in water (IPIECA-IOGP, 2015). 
Solvents are used to dissolve the surfactants, which allows the dispersant to be sprayed onto 
the spilled oil and also facilitates the surfactant’s penetration into the oil slick. 
Dispersant interaction with oil 
The purpose of dispersants is to increase the natural dispersion of the oil by promoting the 
transfer of spilled oil from the surface of the sea into the water column. In addition, oil drop 
lets will have a smaller diameter by adding dispersant than without dispersant, which means 
a larger contact surface available for micro-organisms.